PURPOSE: To provide an angle adjusting mechanism to backward incline a seat- back in an electric motor tricycle, and a height adjusting mechanism in a seat.

CONSTITUTION: A seat leg pipe 32 is provided on the underside of a seat-under 25 through a base bracket 31, back seat frames 27 extending backward are fixedly secured on both sides of the base bracket 31, a seat-back 26 is rotationally movably fitted between the back seat frames 27, and an expansible and contractible mechanical lock 36 is mounted on the underside of seat-under 25 and connected to the lower end of the seat-back 26. By horizontally moving the mechanical lock 36, the angle of the seat-back 26 can be adjusted, and by fixing a height adjusting stopper 40 the optional position of the seat leg pipe 32, the seat can be adjusted on a desired low position.